Method and furnace for heat-treatment of surface coatings on continuously moved strips



KELSEN ET AL CE FOR HEAT Nov. 23, 1954 D. NIC METHOD AND FURNA TREATMENT OF SURFAC COATINGS ON CONTINUOUSLY MOVED STRIPS Flled June 12 1952 2 Sheets-Sheet l Nov. 23, 1954 o. NICKELSEN ETAL ,6 5,

METHOD AND FURNACE FOR HEAT TREATMENT OF SURFACE COATINGS ON CONTINUOUSLY MOVED STRIPS Fzled June 12 1952 2 Sheets-Sheet 2 Zrz,v ant-01 United States Patent" Dag Nickelsen, Knut Anders Nilsen, and Johanwleiigel, Oslo, Norway, assignors to A/S NordiskAluminiumindustri, Oslo, Norway" Application June 12, 1952, Serial No. 293,188 Claims priority, application Sweden June 13, 1951 6 Claims. (Cl. 1l7103) ance of such treatment, the above conditions are only partly or poorly fullfilled and the purpose of the present invention consequently is to overcome the saidmconveniences. It is hereby presumed that possible volatile components of the coating are substantially removed. in advance.

According to the invention this is achieved by subje ctopposite directions.

Conveniently, the gas flow- 1s subdivided lnrthe fo1- lowing manner:

flows are again combined of thecirculating apparatus.

e subdivision'systemdescribed; which is characteristic to the method of'treatment according to the invention, has proved the coating proper. The heating of the clrculatlng gas flow preferably 1s the suctionside of communicated witha'gas path ,directly leaving thevfurnace chamber;

The longitudinal passages which are separated from the furnace chamber'proper preferably extend from the middle ofthe length ofithe furnacexcasing-to points adjacent to the ends of the same; and the evacuationopenings, leading into the the suction side-of the:

passages which extend to=-points "the. furnace casing-open into the opposite each other in chamber.

both strip surfaces are also subjected to substantially equal'pressures whereby the strip is not subjected to any flickering. Of the samereason;- the suction openings are preferably located substantiallyopposite to the side edges of the strip;

In order to avoid the arrangement of-any sourcesinside of the between the pressure side of 1 the rcirculating apparatus and the inlets to thelongitudinalpassages.-

In the heat treatmentof'continuously running strips it is often desirable and necessary; to make the strips run freely through thetreatment furnace, as a contact between the strip 'faces and conveyors or other feeding or supportingv means may damage the strip surfaces-orthe This especially is the case with strips of: comparatively soft-material such as aluminium coatedon. both surfaces. In relatively long *furnaces-a freely suspended strip will, however,- due to gravity give anexcessively great 'sagand consequently require agreat furnace height. A characteristic feature ofthepresent a fo'rm-ofthe side nace without any damage-to thesurfaces;

By'th'e simultaneous 'passing of a plurality of strips; the furnacebottom-may be subdividedinto more sections,- each being' formed as described above. 7,

Theaccompanyingdrawing schematically illustrates an embodiment of a furnace according to the "invention.

Figure .1 is a vertical longitudinal sectional view through the furnace installation.

Figure 2 is a partial horizontal sectional view through one end of the furnace.

Figure 3 is a vertical sectional view along the line III-III of Figure l.

Figure 4 is a vertical sectional view along the line IV--IV of Figure 2.

In the drawing, 1 is the furnace chamber through which the strip 2 is moved in the direction of the arrow indicated in Figure 1. The furnace casing is heat insulated at 3 and is provided with a longitudinal horizontal partition 4 in the top portion, whereby longitudinal passages 5 are formed along the roof of the casing. Further, the furnace is provided with a gas supply passage 6 to the passages 5 and the distribution of the gas from the passage 6 to the passages 5 to each side of the passage 6 is effected by means of an adjustable guide shield 7 cooperating with a battle ridge 8 on which the shield 7 is pivotably mounted.

At the other end, the gas flow through each of the passages 5 is, by means of a partition 9, subdivided into two branch flows 10, which under a deflection of 180 (Figure 4) are fed into the furnace chamber through passages 11, extending slightly obliquely inwardly from the ends and sides of the chamber 1 (Figure 2). point about the middle of the length of the chamber 1, slotlike suction openings 12 are arranged in the side walls, i. e. essentially opposite to the side edges of the strip 2, the said openings 12 being in communication with a suction passage 13 carrying the entire gas flow to the suction side of a fan 14, the pressure side of which is communicating with a conduit 15 carrying the gas flow to a heating battery 16, of conventional design which may be electric, from which the gas flow is again carried through the passage 6 to the passages 5.

In such a construction which provides for a completely closed heating gas circuit, it is presumed that the coating applied to one or both surfaces of the strip 2 does not, during the heating process, give off any volatile components. In certain cases, however, small quantities of such volatile components may be present, for instance released by distillation during the treatment in the furnace. In order to remove such impurities from the gas flow, a blow tube 17 is arranged on the pressure side of the fan 14, the tube 17 being provided with a flap 18. A corresponding addition of fresh gas must then be supplied. If air is used as a heating gas, such supply may be effected through the openings through which the strip 2 is entering and leaving the treatment chamber. By the use of other heating gases suitable provisions must be made for additional supply of gas from an external source.

. In the furnace described, no heating gas loss of any importance normally appears at the open ends of the furnace chamber, as all regard to pressure.

The furnace may with great advantage be used for the purpose of baking, polymerisation, of a lacquer coating on metal strips, when the volatile components (the gas flows are balanced with solvents of the lacquer) are removed in a previous heat treatment, and the present method and'fu'rnace provides for the possibility of obtaining baking periods of unusually short duration at the baking of lacquers, such as those used in the canning industry. Such lacquers usually require a stay period of upwardly to 8 to 15 minutes in the baking zone of the lacquering furnace, whereas the method and furnace according to the present invention enable the use of stay periods of a duration of about 1 minute and even less. Consequently the strip speed is very high, even by a comparatively small furnace length, and the production capacity correspondingly improved.

As an example it maybe mentioned that the strip speeds of 15 to m./min. and a stay period in the baking furnace of a duration of about /2 to 1 min. have been used in practice, at a maximum strip and lacquer temperature which, for instance for lacquers based on phenole may be within the range of 230 to 270 C., preferably at about 250 C. Under such conditions any deposition on the furnace walls, in the passages, etc., are avoided, and at the termination of very long operation periods, the interior of the furnace has presented itself as clean as when the operation started.

As to the meaning of the expression step-by-step subdivision, this is intended to define that the flow is firstly Ata' divided into two partial flows, divided into two sub-partial flows and so on, all flows being then reunited. and fed blower.

We claim:

each of which is then the said to the input of the 1. In a method for the simultaneous heat treatment of coatings on opposite sides of a strip of material, the

steps including passing through a chamber from troducing hot gas in the strip freely continuously inlet to discharge thereof, ma generally horizontal direction across the strip on each side of the strip and from opposite edges of 5 said chamber, surfaces of the aid strip immediately upon its entering mto flowing the hot gas by turbulence over the strip as it advances to approximately mid-length of said chamber, extracting said hot gas from the sides of said chamber at approximately mid-length thereof, flowing additional hot gas by turbulence over both surfaces of the strip as it continues to advance from midlength to discharge of said chamber, said last mentioned turbulent flow being derived from the introduction of hot gases in a generally horizontal direction across the strip, on each side of said strip and from opposite edges of said strip, said gases being extracted from said chamber at approximately mid-length thereof.

2. The method of claim 1, in which the hot gas introduced at the entrance and discharge of the chamber is treated by the steps of recirculating the gas extracted from the furnace at mid-length thereof through a fan,

passing the gas through a heat exchange device to increase the temperature thereof, dividing the flow of hot gas from the heat exchange device into two streams,

one to be led to the entrance end of the chamber, the

other to the discharge end of the chamber, and subture.

3. The method of claim 1, in which the strip is coated with phenolic resin lacquer and baked in the chamber at a temperature of from 230 C. to 270 C.

4. A furnace for sirnultaneons heat treatment of surgated horizont face coatings on a strip of material comprising an elonal furnace chamber, hot gas circulating means comprising a blower to deliver hot gas into passages separated from so arranged a in a generally adjacent eac arranged at 10 remove the chamber, said passages being s to deliver the hot gas into the chamber horizontal direction from each side of and end of said chamber, and further passages the sides of and mid-length of said chamber the hot gas from said chamber and deliver them to the blower suction.

5. The furnace of claim 4, in whch the side walls of the furnace are spaced to give a minimum clearance of the strip as it passes through the 6. The furnace of claim 5, in

furnace. which the side walls converge downwardly from the level at which the strip of material normally passes in order that the edges only of the strip will strike the furnace walls in case the strip sags materially below its normal position.

References Cited in the tile of this patent Number Number UNITED STATES PATENTS 

1. IN A METHOD FOR THE SIMULTANEOUS HEAT TREATMENT OF COATINGS ON OPPOSITE SIDES OF A STRIP OF MATERIAL, THE STEPS INCLUDING PASSING THE STRIP FREELY CONTINUOUSLY THROUGH A CHAMBER FROM INLET TO DISCHARGE THEREOF, INTRODUCING HOT GAS IN A GENERALLY HORIZONTAL DIRECTION ACROSS THE STRIP ON EACH SIDE OF THE STRIP AND FROM OPPOSITE EDGES OF SAID STRIP IMMEDIATELY UPON ITS ENTERING INTO SAID CHAMBER, FLOWING THE HOT GAS BY TURBULENCE OVER THE SURFACES OF THE STRIP AS IT ADVANCES SO APPROXIMATELY MID-LENGTH OF SAID CHAMBER, EXTRACTING SAID HOT GAS FROM THE SIDES OF SAID CHAMBER AT APPROXIMATELY MID-LENGTH THEREOF, FLOWING ADDITIONAL HOT GAS BY TURBULENCE OVER BOTH SURFACES OF THE STRIP AS IT CONTINUES TO ADVANCE FROM MIDLENGTH TO DISCHARGE OF SAID CHAMBER, SAID LAST MENTIONED TURBULENT FLOW BEING DERIVED FROM THE INTRODUCTION OF HOT GASES IN A GENERALLY HORIZONTAL DIRECTION ACROSS THE STRIP, ON EACH SIDE OF SAID STRIP AND FROM OPPOSITE EDGES OF SAID STRIP, SAID GASES BEING EXTRACTED FROM SAID CHAMBER AT APPROXIMATELY MID-LENGTH THEREOF. 